smc/mcon is a SAP Parameter attribute which is used to control Switch on/off synchroneous matchode writing information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
You can use this parameter to switch the synchronous update of
matchcodes on or off.
1: The synchronous matchcode update is switched on
Otherwise, the synchronous matchcode update is switched off
Caution
This parameter affects only matchcode IDs that are defined with the
update type 'S' in the Data Dictionary. All other matchcodes, in
particular the transparent ones, are unaffected by this parameter.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.